Vasovagal syncope, or neurally-mediated syncope, is a complex fainting disorder which affects a significant number of people. The degree to which individuals are affected by vasovagal syncope varies, and some individuals experience multiple episodes of vasovagal syncope. Accordingly, more aggressive treatments are required for such individuals.
Several treatments for vasovagal syncope are known in the art. For example, oral pharmacological therapies, such as administration of beta-blockers, have been used. However, oral therapy alone is inadequate to prevent sudden episodes of vasovagal syncope. Further, the therapeutic efficacy of such treatments remains unclear, as it is difficult to assess efficacy of such treatments in randomized trials.
Another proposed treatment for vasovagal syncope is pacemaker therapy alone. For example, see Markowitz et al., U.S. Pat. No. 5,501,701, which teach detection and treatment of vasovagal syncope using a device comprising a pacemaker and means for detecting syncopal episodes based on decreased heart rate.
Pacing therapies used in conjunction with various sensors of physiological parameters are well known in the art. A pacemaker using P-wave sensors is taught by Knudson et al., U.S. Pat. No. 4,313,442. A pacemaker responsive to changes in Q-T interval is taught in Rickards, U.S. Pat. No. 4,228,803. Sensed atrial and ventricular signals are used in the pacing device of Funke, U.S. Pat. No. 4,312,355. Alcidid, U.S. Pat. No. 4,009,721 teaches a pacemaker controlled by blood pH. A pacemaker which uses sensed molecular blood oxygen levels is taught by Wirtzfeld et al., U.S. Pat. No. 4,202,339. A pacemaker which uses sensed respiratory rates is taught by Krasner, U.S. Pat. No. 3,593,718. Pacer systems based on motion sensors are taught by Anderson et al., U.S. Pat. No. 4,428,378. Cohen, U.S. Pat. No. 3,358,690 and Zacouto, U.S. Pat. No. 3,857,399 teach pacing responsive to sensed cardiac pressure.
However, pacemaker therapy alone has been found to lack efficacy in many patients suffering from vasovagal syncope. Combination therapy, such as atrioventricular pacing with intravenous administration of beta-blockers, is also known. Given the sudden and intermittent occurrence of syncopal episodes, however, normal intravenous routes of drug infusion are often not available at the occurrence of such events and therefor too late to be of practical use.
Hence, there still exists a need for an improved method of treating dysautonomic syncope which is capable of accurately detecting the onset of the syncopal episode and administers treatment in accurate and efficient manner to prevent the occurrence thereof.